1. Technical Field
The invention relates to an electrophoretic display sheet production process, an electrophoretic display sheet, an electrophoretic display device, and an electronic apparatus.
2. Related Art
In a dispersion system where microparticles are dispersed in a liquid, it is generally known that the microparticles migrate (are electrophoresed) in the liquid by a Coulomb force caused by applying an electric field. This phenomenon is called electrophoresis, and, recently, electrophoretic display devices, which display desired information (image) using the electrophoresis, have been attracting attentions as new display devices.
The electrophoretic display devices have characteristics that they have a display memory property at the time of stoppage of voltage application and a wide viewing angle and are capable of high contrast displaying at low power consumption.
The electrophoretic display device is a reflection-type display using natural light as a light source. In order to realize high visibility, high transparency at its light-transmitting portion, high reflectance at its light-reflecting portion, and high absorption at its light-absorbing portion are required to be achieved.
As a known electrophoretic display device, JP-A-2007-058151 discloses an electrophoretic display device where a microcapsule-containing layer including multiple microcapsules and a binder is disposed between and joined to a pair of substrates.
Here, in the microcapsules, electrophoretic particles are dispersed in an electrophoretic dispersion liquid sealed in a wall material (forming shells). As the material of the shells, a relatively flexible material, for example, a composite material of gum arabic and gelatin has been widely used. When the shells are made of a flexible material, the microcapsules in the microcapsule-containing layer disposed between two substrates are compressed by the substrates and thereby deformed. Therefore, in the resulting microcapsule-containing layer, microcapsules are crushed in the vertical direction (stone-wall structure).
The microcapsules having shells made of a flexible material are insufficient in pressure resistance (to endure an applied pressure without causing crushing of the microcapsules) and bleed resistance (to prevent dissipation of the dispersion liquid sealed in the microcapsules). As a result, breakage of the microcapsules or leakage of the dispersion is easily caused by impact or pressing force applied during the display device is used or stored, and therefore there is a problem of difficulty in operating the electrophoretic display device stably for a long time.
In order to solve such a problem, for example, proposed is an electrophoretic display device including microcapsules having relatively strong shells made of a plurality of layers: a layer made of an epoxy resin and a layer made of a melamine resin (for example, see JP-A-2008-165191).
By forming the microcapsules in such a structure, the approximately spherical shapes of the microcapsules can be maintained even when the microcapsule-containing layer containing the microcapsules is disposed between the two substrates. Therefore, breakage of the microcapsules or leakage of the dispersion liquid can be surely prevented even if impact or pressing force is applied during the display device is used or stored.
In the electrophoretic display device having approximately spherical microcapsules in the state that the microcapsule-containing layer is disposed between two substrates, in order to obtain higher contrast, it is necessary to arrange the microcapsules in the microcapsule-containing layer so as to be in contact with one another in the lateral direction and to form a single layer without overlapping in the thickness direction.